This invention is broadly related to the field of electronic musical instruments, particularly electronic organs or other electronic musical instruments having a keyboard such as electric pianos, accordians and the like. The term "organ" as used throughout the specification and claims in intended in a generic sense to include these other electronic musical instruments. In addition, reference to the actuation of key switches or coupler switches and the like is intended to cover the actuation of such switches by whatever means may be employed, such as directly by action of the musician's fingers or indirectly through intervening levers, apertures, switch closings, touch responsive switches, etc.
In the design of electronic organs, an attempt is made to faithfully reproduce as nearly as possible the musical sounds and tones which are developed by true pipe organs in response to the playing of the electronic organ by a musician. In order to simulate as many pipe organ sounds as possible, electronic organs have included a large number of switches, wiring cables, and the like, to permit the utilization of intramanual and intermanual couplers employed with at least two manual keyboards and a single pedalboard. A pair of pedalboards and an even larger number of manual keyboards are used in more complex electronic organs. The manual keyboards generally encompass several octaves and the pedalboards usually one or more octaves. In addition, a typical electronic organ includes a relatively large number of playing stops or tabs which are associated with each of the keyboards to permit selection of different organ voices for the tones produced by those keyboards by changing the timbre, tone quality and the like.
The large number of interconnections between the keyboards, couplers, stops and tone generators for such electronic organs results in substantial complexity and assembly costs. In addition, the maze of cabling and wires and connection points within the organ circuitry increases the possibility of failure and makes servicing of the instrument difficult and expensive.
Attempts to reduce the complexity of electronic organs, and in particular to reduce the large amounts of interconnecting wiring and cables and the terminal connections for such interconnecting wiring, has resulted in the development of multiplexing arrangements for replacing much of the wiring hitherto required. One type of digital multiplexing system which has been employed utilizes a scanning system to repetitively scan the switches for each key and coupler position in all of the keyboards and couplers in series to produce a single series train of time-division multiplexed pulses, each of which represents the condition of operation of a particular key or coupler in the instrument. This pulse train can be transmitted on a single wire to a de-multiplexing section of the organ where the pulses are used to operate keyers to produce tones representative of the keys which have been actuated. For an organ with a large number of manual keyboards and pedalboards, this sequential scanning of all of the possible keys and couplers in series results in a very long pulse train for each cycle of operation of the scanning system. The length of each pulse train cycle is directly proportional to the number of notes in an octave times the number of octaves times the number of keyboards and pedalboards used in the organ. This results in a relatively complex de-multiplexing section of the organ, even though such a system results in substantial economies of wiring complexity over electronic organs not employing a multiplexing system.
Another type of multiplexing system, which has been developed in the prior art, employs a separate transmission line between a multiplexing portion and a de-multiplexing portion for each different octave in each of the different keyboards and pedalboards. The twelve notes in each of these octaves are represented by twelve time positioned pulses representing the twelve semi-tones of the corresponding octave. All of the octaves of all of the keyboards and pedalboards of the organ are transmitted simultaneously on the respective octave leads as time-division multiplexed note pulses. For an organ having two manual keyboards, each with a capacity of five octaves, and a pedalboard, this type of system results in eleven transmission lines between the multiplexing portion of the organ and the de-multiplexing portion. In addition, if intramanual and intermanual couplers are provided, a provision must be made for transferring pulses on one of the octave leads to one or more of the others by means of wiring and logic interconnections between the different leads. The result is a relatively large number of wires and wiring interconnections, although not as many as are required for a standard electronic organ which does not employ any multiplexing at all.
It is desirable to provide an electronic musical instrument such as an electronic organ which does not require a large mass of conductors and connection points to provide electrical connections between the keys of each of the keyboards (manual and pedal) and the tone generators of the organ. In addition, it is desirable to employ a system for driving the keyer sections of an electronic organ in parallel from a multiplexed signal train while using different numbers of individual keyers for the different tone qualities, such as flute and string, produced by the organ.
It is also desirable to reduce the number of pulses in the multiplex signal train which are necessary to convey all of the information from all of the keyboards to all of the keyers, while at the same time minimizing the number of lines interconnecting the multiplexer portion of the organ with the de-multiplexer portions.